Hunting for pentaquarks

Abstract

According to a news release dated 16 April 2005, recent experimental data from JLAB, the Thomas Jefferson National Accelerator facility in Newport News, Virginia, USA point to the absence of the pentaquark called Q+, at the place where it was expected. This surprising result due to the CLAS collaboration (where CLAS stands for the CEBAF Large Acceptance Spectrometer; CEBAF stands for the Continuous Electron Beam Accelerator Facility, which was the name of JLAB) contradicts the findings of several prior experiments, including some of its own, which indicated that at least one kind of pentaquark exists in the mass range 1525-1555 MeV/c2 (for a review, see Hicks1), while none of the experiments could definitively prove its existence. This recent experiment was based on a high energy photon beam on a liquid hydrogen target. It had considerably greater statistics; in fact, two orders of magnitude greater than a similar experiment in Germany carried out by the SAPHIR collaboration at the ELSA (Electron Stretcher Accelerator) in Bonn2, which had seen evidence for the existence of pentaquarks. At JLAB, work is continuing in the hunt for pentaquarks with even higher statistics, and the data are being analysed with the possibility of publication of results later this year. The CLAS collaboration is likely to gather more data in 2006 by searching for other pentaquark candidates.